Various sporting rifles are known in the state of the art with a fork system incorporated into the chamber that articulates with the butt.
Thus, Utility Model No 9201525, “PIEZA DE CABEZA DEL TUBO DE COMPRESIóN EN CARABINAS DE AIRE COMPRIMIDO”, is known from 1992, in the name of NORBERTO ARIZMENDI, S.A., which refers to a compression tube head piece in compressed air rifles, in particular, a head piece of closing front of the compression tube with a peculiar configuration especially fitted for execution moulded in plastic and generally comprising a fixable core inside said tube, which is fitted with the corresponding paraxial pitch compressed air projector and by the front fork prongs that support the barrel articulation shaft, characterised in that it comprises a single-piece moulded plastic body and in that one of said prongs has an anti-rotation groove with a securing nut for the point of a barrel articulation screw-shaft, the tail of which has a plug-in structure on which the following elements in particular are defined: a pair of peripheral annular channels for reception of the corresponding sealing O-rings; a pair of crosswise drilled for two metal retaining pins, their ends housed inside orifices in the compression tube wall; a pair of blind lower oblique housings in symmetrical contraposition in the same transversal section, oblique housings that have reciprocal polygonal section of the periphery of the two metal nuts it can hold inside; a leading stepped front producing a seating projection for the limiting stop in the closed barrel position; a front channel around said air passage for holding an O-ring; and a front blind hole located in said projection for receiving the double-chamfer retainer metal point for barrel closure.
European Patent No 0260204 “GAS-OPERATED AUTOMATIC RIFLE WITH BREAKING BARREL OR NOT”, in name of the firm EXBRAYAT & CIE SOCIÉTÉ EN COMMANDITE SIMPLE, of 1987 also belongs to the state of the art, which relates to a gas-operated automatic rifle. According to the invention, the barrel is mounted with a capacity for forward movement in relation to the magazine tube; the front part of the barrel receives, in its lower part, a sleeve forming internally a gas expansion chamber in communication with the barrel; the magazine tube has an extension partially engaging into the sleeve, without closing the orifice for the passage of the gases; a piston slides in the sleeve under the thrust of the gases and acts counter to the barrel recovery spring by a means for the purpose of releasing the barrel and displacing it in relation to the magazine tube; the means is secured to a pair of rods sliding along the magazine tube and the rocker in order to allow the cocking of the striker and the return of the means for lifting cartridges into the barrel tube.
Spanish Patent No ES2194564, “BARREL ARTICULATION DEVICE FOR A COMPRESSED AIR SPORTING RIFLE OR PISTOL WITH BREAKING BARREL” from the same applicant firm, belongs to the state of the art, which refers to a barrel articulation device for a compressed air sporting rifle or pistol with breaking barrel that comprises a barrel box connected to the rear end of the barrel, with articulation and a closing catch with respect to a fork, connected to the front end of a compression chamber. Said box is connected to a lever mechanism that compresses a piston in the compression chamber, with said fork comprising an internal moulded piece that concentrates most complex configurations, that is inserted adjusted and joined to a portion of the mouth of said compression chamber, which is a metal tube that exactly covers said internal fork piece, with the barrel box, also obtained by moulding, with a rear part of the barrel ready for insertion.